SIMPLE ISOTOPE-DILUTION ASSAY FOR PROPIONIC-ACID AND ISOVALERIC ACID

A gas chromatographic-mass spectrometric method is described for the a ssay of propionic acid and of isovaleric acid in physiological fluids by isotope dilution. The acids are derivatized to the pentafluorobenzy l esters to decrease volatility to render them suitable for GC-MS anal ysis. The following reference values were found. Propionic acid: plasm a 0.54 +/- 0.38 mu mol/l (n = 13, range 0.03-1.38 mu mol/l), urine 1.7 +/- 1.6 mu mol/mmol creatinine (n = 9, range 0.1-4.9 mu mol/mmol crea tinine). Isovaleric acid: plasma 0.89 +/- 0.93 mu mol/l (n = 10, range 0.01-3.03 mu mol/l), urine 0.38 +/- 0.51 mu mol/mmol creatinine (n = 10, range 0.01-1.70 mu mol/mmol creatinine).